Cable connection structure, connecting power cable, and method for manufacturing the cable connection structure

Abstract

The cable connection structure comprises a conductor connection portion connecting the conductors of a pair of power cables, an inner semiconductive layer that is semiconductive and arranged to cover the outer periphery of the conductor connection portion, an insulating layer that is insulating and arranged to cover the outer periphery of the inner semiconductive layer, the insulating layer having an inner circumferential surface facing the inner semiconductive layer and an outer circumferential surface opposite the inner circumferential surface, and an outer semiconductive layer that is semiconductive and arranged to cover the outer periphery of the insulating layer, the insulating layer comprising a base polymer containing propylene units, a modified polymer that contains propylene units and is modified with at least one selected from unsaturated organic acids and derivatives thereof, and a thermoplastic elastomer, wherein the ratio of the storage modulus of the inner sample of the insulating layer to the storage modulus of the outer sample is 1.1 or more and 2.5 or less, and the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less.

Description

[Technical Field]

[0001] The present disclosure relates to a cable connection structure, a connecting power cable, and a method for manufacturing a cable connection structure. [Background technology]

[0002] When manufacturing a power cable that will be laid over a long distance, multiple power cables may be connected in a factory to produce a linked power cable having a desired distance. The cable connection structure in this case is called a "factory joint (FJ)" (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-56039 Summary of the Invention

[0004] According to one aspect of the present disclosure, a power cable includes a conductor connection part connecting the conductors of a pair of power cables, an internal semiconductive layer provided to cover an outer periphery of the conductor connection part and having semiconductivity, an insulating layer provided to cover an outer periphery of the internal semiconductive layer, having insulating properties, and having an inner circumferential surface facing the internal semiconductive layer and an outer circumferential surface opposite to the inner circumferential surface, and an external semiconductive layer provided to cover an outer periphery of the insulating layer and having semiconductivity, wherein the insulating layer includes a base polymer containing a propylene unit, a modified polymer containing a propylene unit and modified with at least one selected from unsaturated organic acids and derivatives thereof, and a thermoplastic elastomer, and wherein a storage modulus of the insulating layer relative to a storage modulus of an outer sample of the insulating layer is a ratio of the storage modulus of the inner sample to the volume resistivity of the outer sample is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less, wherein the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the internal semiconducting layer, and the inner sample of the insulating layer is taken from a position 0.3 mm from the inner peripheral surface toward the outer peripheral surface, the storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, and the volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90°C and a DC electric field of 80 kV / mm. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a cable connection structure according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a flow chart illustrating a method for manufacturing a linked power cable according to one embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram showing the second heating step. [Figure 4] FIG. 4 is a diagram showing the temperature at the collection position of the outer sample and the temperature at the collection position of the inner sample in the second heating step of sample A3. [Figure 5]FIG. 5 is a diagram showing the temperature at the collection position of the outer sample and the temperature at the collection position of the inner sample in the second heating step of sample B1. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] An object of the present disclosure is to improve the flexibility, strength and insulating properties of an insulating layer in a cable connection structure.

[0007] [Effects of this disclosure] According to the present disclosure, it is possible to improve the flexibility, strength, and insulating properties of the insulating layer in a cable connection structure.

[0008] [Description of the embodiments of the present disclosure] <Knowledge gained by the inventors> First, the findings of the inventors will be outlined.

[0009] In a cable connection structure configured as an FJ, an insulating layer is formed by wrapping insulating tape around the outer periphery of an internal semiconductive layer. If voids occur between the multiple wraps of insulating tape in such an insulating layer, the insulating properties of the insulating layer may be reduced due to the voids. Therefore, after the insulating layer formation process, a heating process (the second heating process described below) is carried out. This allows the multiple wraps of insulating tape in the insulating layer to be fused together by heating. As a result, it is possible to suppress the occurrence of voids in the insulating layer.

[0010] The inventors have investigated polypropylene as a base polymer for the insulating layer of the cable connection structure, and have found that an insulating layer containing polypropylene can provide good insulation even in a non-crosslinked state.

[0011] However, as a result of investigations by the inventors, it was found that the insulating layer of a cable connection structure containing polypropylene as the base polymer causes the following new problems.

[0012] Polypropylene has a higher melting point and higher thermal resistance than polyethylene, so that the temperature inside the insulating layer is less likely to rise in the heating step after the insulating layer formation step.

[0013] Therefore, the inventors have considered increasing the temperature at which the insulating layer is heated from the outside by a heater of a heating device in order to melt the insulating tape all the way to the inside of the insulating layer.

[0014] However, when the temperature at which the insulation layer is heated from the outside by the heater of the heating device is excessively high, the outside of the insulation layer is overheated and thermally deteriorated. As a result, the elasticity and volume resistivity of the outside of the insulation layer become excessively low. As a result, the insulation and mechanical properties required for a cable connection structure cannot be obtained.

[0015] On the other hand, the inventors have investigated the use of induction heating to heat the conductor connection portion in the heating step after the insulating layer formation step, in addition to heating with a heater in the heating device. This allows the inside of the insulating layer to be heated without excessively increasing the heating temperature of the heater in the heating device. As a result, the temperature difference between the outside and inside of the insulating layer can be reduced.

[0016] However, when the temperature difference between the outside and inside of the insulating layer was small, the outside and inside of the insulating layer were cooled evenly during cooling after heating. As a result, the crystallinity of the base polymer on the outside of the insulating layer and the crystallinity of the base polymer on the inside of the insulating layer were similarly high. Due to this high crystallinity, the elasticity of the insulating layer was uniformly high in the thickness direction. In this case, it was difficult to ensure sufficient flexibility of the connecting power cable having the cable connection structure when it was bent. As a result, there were restrictions on the reel diameter when the connecting power cable was wound around the reel.

[0017] Therefore, after extensive research, the inventors improved the resin components that make up the insulating layer and also improved the second heating step in a new manufacturing method, thereby succeeding in achieving the desired distribution of elasticity in the thickness direction of the insulating layer of the cable connection structure while making the insulating properties of the insulating layer of the cable connection structure uniform in the thickness direction of the insulating layer.

[0018] The present disclosure is based on the above-mentioned findings of the inventors.

[0019] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0020] [1] A cable connection structure according to one aspect of the present disclosure includes: a conductor connection portion connecting the conductors of the pair of power cables; an inner semiconductive layer that is provided so as to cover an outer periphery of the conductor connection portion and has semiconductivity; an insulating layer that is provided so as to cover an outer periphery of the internal semiconductive layer, has insulating properties, and has an inner circumferential surface facing the internal semiconductive layer and an outer circumferential surface opposite to the inner circumferential surface; an outer semiconductive layer that is provided so as to cover the outer periphery of the insulating layer and has semiconductivity; Equipped with The insulating layer is a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, a ratio of the storage modulus of an inner sample of the insulating layer to the storage modulus of an outer sample of the insulating layer is 1.1 or more and 2.5 or less; a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the inner semiconducting layer, the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0021] [2] In the cable connection structure described in [1] above, When the total content of the base polymer, the modified polymer, and the thermoplastic elastomer in the insulating layer is 100 parts by mass, the content of the modified polymer in the insulating layer is 1 part by mass or more and 10 parts by mass or less; The content of the thermoplastic elastomer in the insulating layer is 10 parts by mass or more and 45 parts by mass or less. According to this configuration, it is possible to stably achieve both a desired distribution of elasticity and uniformity of insulation in the thickness direction of the insulating layer.

[0022] [3] In the cable connection structure described in [1] or [2] above, The thermoplastic elastomer includes a styrene-based elastomer. This configuration allows short chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C), thereby improving the compatibility between the base polymer (A) and the thermoplastic elastomer (C).

[0023] [4] In the cable connection structure according to any one of [1] to [3] above, The thermoplastic elastomer includes an olefin-based elastomer. This configuration allows short chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C), thereby improving the compatibility between the base polymer (A) and the thermoplastic elastomer (C).

[0024] [5] In the cable connection structure according to any one of [1] to [4] above, the storage modulus of the inner sample of the insulating layer is 650 MPa or more and 900 MPa or less; The storage modulus of the outer sample of the insulating layer is 280 MPa or more and 670 MPa or less. This configuration allows the cable connection structure to have both rigidity and flexibility.

[0025] [6] In the cable connection structure according to any one of [1] to [5] above, The insulating layer has a thickness of 3 mm or more. According to this configuration, even when a connecting power cable having a cable connection structure is used in high voltage applications, it is possible to stably achieve both flexibility of the insulating layer and insulation properties of the insulating layer.

[0026] [7] A connecting power cable according to one embodiment of the present disclosure includes: The present invention includes at least one cable connection structure according to any one of [1] to [6]. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0027] [8] A method for manufacturing a cable connection structure according to one embodiment of the present disclosure includes: forming a conductor connection portion by connecting the conductors of the pair of power cables; forming an inner semiconductive layer having semiconductivity so as to cover an outer periphery of the conductor connection portion; forming an insulating layer having insulating properties so as to cover an outer periphery of the internal semiconducting layer; forming an outer semiconductive layer having semiconductivity so as to cover an outer periphery of the insulating layer; heating the insulating layer and the outer semiconducting layer and then cooling; Equipped with The step of forming the insulating layer includes: preparing an insulating tape containing a resin composition; a step of winding the insulating tape around an outer periphery of the internal semiconductive layer to form an inner periphery surface of the insulating layer facing the internal semiconductive layer and an outer periphery surface opposite to the inner periphery surface; and In the step of preparing the insulating tape, The resin composition includes: a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; preparing an insulating tape comprising: The step of heating and then cooling the insulating layer and the outer semiconducting layer comprises: the insulating layer is heated and then cooled so that a ratio of the storage elastic modulus of an inner sample of the insulating layer to that of an outer sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to that of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the inner semiconducting layer, the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0028] [9] In the method for manufacturing a cable connection structure described in [8] above, The insulating layer is heated from a region close to the outer peripheral surface of the insulating layer while the conductor connection portion is subjected to electromagnetic induction heating, thereby heating the insulating layer also from a region close to the inner peripheral surface of the insulating layer. According to this configuration, the insulating tape on the inside of the insulating layer can be stably fused while suppressing thermal deterioration on the outside of the insulating layer.

[0029] [Details of the embodiments of the present disclosure] Next, one embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0030] <One embodiment of the present disclosure> (1) Overview of connecting power cables and cable connection structure A coupled power cable 10 and a cable connection structure (cable connection portion) 20 according to a first embodiment of the present disclosure will be described with reference to Fig. 1. In Fig. 1, a side surface of the power cable 100 that has been peeled off in stages is shown. The lower side of Fig. 1 is omitted.

[0031] As shown in FIG. 1, the connected power cable 10 of this embodiment is configured as an underwater cable laid on the bottom of the water (ocean bottom), for example, and includes a plurality of power cables 100 and at least one cable connection structure 20.

[0032] (power cable) The power cable 100 is configured as a solid insulated cable that is a high-voltage power transmission cable.

[0033] The power cable 100 includes, for example, the conductor 110, a cable inner semiconductive layer 120, a cable insulating layer 130, a cable outer semiconductive layer 140, a water absorbing layer (not shown), a cable metal tube 150, and a cable sheath 160, arranged from the central axis of the conductor 110 toward the outer periphery of the power cable 100. The base polymer included in the cable insulating layer 130 is, for example, polypropylene.

[0034] One of the pair of power cables 100 may be referred to as a "first power cable 100a," and the other power cable 100 may be referred to as a "second power cable 100b."

[0035] (cable connection structure) As shown in FIG. 1, the cable connection structure 20 includes, for example, a first power cable 100a, a second power cable 100b, a conductor connection portion 210, an inner semiconductive layer 220, an insulating layer 230, an outer semiconductive layer 240, a water-absorbing tape layer 242, a metal tube (protective tube) 250, and an anticorrosion layer (connection portion sheath) 260, in this order from a region close to the conductor connection portion 210 toward the outside.

[0036] At the conductor connection portion 210, the conductor 110 of the first power cable 100a and the conductor 110 of the second power cable 100b are connected.

[0037] The internal semiconductive layer 220 is provided so as to cover the outer periphery of the conductor connection portion 210. The internal semiconductive layer 220 has semiconductivity.

[0038] The insulating layer 230 is provided so as to cover the outer periphery of the internal semiconductive layer 220. The insulating layer 230 has insulating properties. The insulating layer 230 has an inner circumferential surface facing the internal semiconductive layer 220 and an outer circumferential surface opposite the inner circumferential surface.

[0039] The outer semiconductive layer 240 is provided so as to cover the outer periphery of the insulating layer 230. The outer semiconductive layer 240 has semiconductivity.

[0040] In this embodiment, the base polymer in each of the inner semiconductive layer 220, the insulating layer 230, and the outer semiconductive layer 240 is, for example, polypropylene.

[0041] In the cable connection structure 20, the portions other than the inner semiconductive layer 220, the insulating layer 230, and the outer semiconductive layer 240 can be configured as a general FJ configuration, for example, as described in JP 2023-065809 A. Note that the metal pipe 250 and the anticorrosion layer 260 do not necessarily have to be provided.

[0042] (Specific dimensions, etc.) The specific dimensions of the cable connection structure 20 are not particularly limited, but for example, the diameter of the conductor connection portion 210 is 5 mm to 60 mm, the thickness of the inner semiconductive layer 220 is 0.5 mm to 3 mm, the thickness of the insulating layer 230 is 3 mm to 35 mm, and the thickness of the outer semiconductive layer 240 is 0.5 mm to 3 mm. The DC voltage applied to the connected power cable 10 of this embodiment is, for example, 20 kV or higher.

[0043] (2) Resin composition constituting the insulating tape The insulating layer 230 is formed, for example, by wrapping an insulating tape around the outer periphery of the internal semiconductive layer 220. The insulating tape contains a resin composition. The resin composition of this embodiment contains, for example, a base polymer (A), a modified polymer (B), a thermoplastic elastomer (C), and other additives.

[0044] Hereinafter, the base polymer (A), the modified polymer (B), and the thermoplastic elastomer (C) are also referred to as "resin components."

[0045] (Base polymer (A)) The base polymer (base resin) (A) refers to the resin component that constitutes the main component of the resin composition. The "main component" refers to the component that is contained in the largest amount.

[0046] The base polymer (A) of this embodiment contains, for example, at least a propylene unit as a monomer unit.

[0047] That is, when the resin composition of this embodiment is analyzed by a nuclear magnetic resonance (NMR) device, propylene units are detected as monomer units derived from the base polymer (A).

[0048] The base polymer (A) is, for example, made of polypropylene (propylene-based resin, also called PP) having propylene units in the main chain. Examples of polypropylene include homopolypropylene (homoPP), random polypropylene (randomPP), and block polypropylene (blockPP).

[0049] By analyzing the resin composition of this embodiment by NMR, for example, when the base polymer (A) is a random PP or a block PP, propylene units and ethylene units derived from the random PP or the block PP are detected, and when the base polymer (A) is a homo PP, propylene units derived from the homo PP are detected.

[0050] From the viewpoint of obtaining high insulating properties in the insulating layer 230, the base polymer (A) may be random PP. Homo PP has a higher crystalline content than random PP, and can obtain high insulating properties. However, an insulating layer 230 containing homo PP may cause cracks within or between crystals. For this reason, homo PP may not obtain the insulating properties it inherently possesses. In contrast, random PP contains ethylene units, and therefore has a lower crystalline content. However, an insulating layer 230 containing random PP is less likely to crack due to coarse crystallization. As a result, random PP can obtain higher insulating properties than homo PP.

[0051] When the base polymer (A) is a random PP, the ethylene unit content in the random PP may be, for example, 0.5% by mass or more and 15% by mass or less. By setting the ethylene unit content to 0.5% by mass or more, it is possible to suppress the growth of coarse spherulites. On the other hand, by setting the ethylene unit content to 15% by mass or less, it is possible to suppress a decrease in melting point and to stably realize use in a non-crosslinked or slightly crosslinked state.

[0052] In this embodiment, the stereoregularity of the polypropylene is not particularly limited, but may be, for example, isotactic. Here, if the stereoregularity of the polypropylene is atactic, the polypropylene will not crystallize. In contrast, isotactic polypropylene is polymerized with a Ziegler-Natta catalyst and is a versatile material. The isotactic stereoregularity of the composition can suppress a decrease in melting point. This allows a predetermined crystallinity to be easily obtained, resulting in high insulating properties.

[0053] In this embodiment, the storage modulus of the base polymer (A) alone is, for example, 800 MPa or more and 1700 MPa or less. The measurement method and conditions for the "storage modulus of the base polymer (A) alone" are the same as those for the storage modulus of the insulating layer 230 described later.

[0054] The melt flow rate (MFR) of the base polymer (A) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 5.0 g / 10 min or less, or 0.1 g / 10 min or more and 2.0 g / 10 min or less. The "MFR" here refers to a value measured in accordance with JIS K7210 at a temperature of 190°C and a load of 2.16 kg. By setting the MFR of the base polymer (A) within the above range, the phase structure described below can be easily formed in the insulating layer 230.

[0055] The melting point of the base polymer (A) is not particularly limited, but may be, for example, 130° C. or higher and 165° C. or lower. This makes it possible to easily form a phase structure described below when the base polymer (A) is mixed with at least one of the modified polymer (B) and the thermoplastic elastomer (C).

[0056] (Modified polymer (B)) The modified polymer (B) contains propylene units as the main chain and is modified with at least one selected from unsaturated organic acids and derivatives thereof.

[0057] When the modified polymer (B) contains propylene units, the compatibility of the base polymer (A) and the modified polymer (B) when they are mixed can be improved.

[0058] By modifying the modified polymer (B) with an unsaturated organic acid containing a polar group, a polar group can be introduced into the resin composition. This allows the polar groups dispersed in the insulating layer 230 formed from the insulating tape containing the resin composition to trap space charge. In other words, local accumulation of space charge in the insulating layer 230 can be suppressed. As a result, the insulating properties of the insulating layer 230 can be improved.

[0059] Specifically, the modified polymer (B) may be, for example, an unsaturated carboxylic acid-modified polypropylene in which polypropylene is modified with at least one of an unsaturated carboxylic acid and its derivatives. Examples of unsaturated carboxylic acids and their derivatives include acrylic acid, methacrylic acid, crotonic acid, maleic acid, cinnamic acid, itaconic acid, citraconic acid, fumaric acid, and anhydrides thereof.

[0060] Among these, the modified polymer (B) may be modified with, for example, maleic anhydride. Maleic anhydride has a large number of polar groups per molecular weight. This ensures that the number of polar groups in the modified polymer (B) is sufficient even if the content of maleic anhydride in the modified polymer (B) is small.

[0061] The modification amount of at least one of the unsaturated carboxylic acid and its derivative in the modified polymer (B) (hereinafter simply referred to as the modification amount) is not particularly limited, but may be, for example, 0.1% by mass or more and 10% by mass or less. The "modification amount" here refers to the copolymerization ratio (content) of at least one of the unsaturated carboxylic acid and its derivative in the modified polymer (B). By setting the modification amount to 0.1% by mass or more, it is possible to stably suppress the accumulation of space charge in the insulating layer 230. On the other hand, by setting the modification amount to 10% by mass or less, it is possible to improve the compatibility between the modified polymer (B) and the base polymer (A).

[0062] In this embodiment, the storage modulus of the modified polymer (B) alone is, for example, 1000 MPa or more and 1900 MPa or less. The measurement method and conditions for the "storage modulus of the modified polymer (B) alone" here are the same as those for the storage modulus of the insulating layer 230 described later.

[0063] The MFR of the modified polymer (B) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 500 g / 10 min or less, or 1 g / 10 min or more and 300 g / 10 min or less. The measurement conditions for the MFR of the modified polymer (B) here are the same as those described for the MFR of the base polymer (A). When the MFR of the modified polymer (B) is within the above range, the phase structure described below can be easily formed when the base polymer (A) and the modified polymer (B) are mixed.

[0064] The melting point of the modified polymer (B) is not particularly limited, but may be, for example, 130° C. or higher and 165° C. or lower, which allows the phase structure described below to be easily formed when the base polymer (A) and the modified polymer (B) are mixed.

[0065] (Thermoplastic elastomer (C)) The thermoplastic elastomer (C) has lower crystallinity than the base polymer (A) having propylene units, and the thermoplastic elastomer (C) can suppress excessive crystal growth of the base polymer (A) and impart flexibility to the insulating layer 230.

[0066] Examples of the thermoplastic elastomer (C) include amide-based, ester-based, olefin-based, styrene-based, urethane-based, vinyl chloride-based, fluorine-based, etc. Among these, the thermoplastic elastomer (C) may be at least one of a styrene-based polymer and an olefin-based elastomer.

[0067] (styrene elastomer) The thermoplastic elastomer (C) may contain, for example, a styrene-based elastomer. This allows short-chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C). As a result, the compatibility between the base polymer (A) and the thermoplastic elastomer (C) can be improved.

[0068] In this embodiment, the styrene-based elastomer is, for example, a copolymer containing styrene units as hard segments and at least one monomer unit selected from ethylene units, propylene units, butylene units, and isoprene units as soft segments.

[0069] Examples of styrene-based elastomers include styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-styrene block copolymer (SES), styrene-ethylene-propylene copolymer (SEP), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, styrene-ethylene-butylene olefin crystalline block copolymer, etc. Two or more of these may be used in combination.

[0070] "Hydrogenated" here means that hydrogen has been added to the double bond. For example, "hydrogenated styrene butadiene styrene block copolymer" means a polymer in which hydrogen has been added to the double bond of a styrene butadiene styrene block copolymer. No hydrogen has been added to the double bond of the aromatic ring of styrene. "Hydrogenated styrene butadiene styrene block copolymer" can be rephrased as styrene ethylene butylene styrene block copolymer (SEBS).

[0071] The styrene-based elastomer may be, for example, a hydrogenated material that does not contain double bonds in its chemical structure except for aromatic rings. If a non-hydrogenated material is used, the resin component may be thermally degraded during molding of the resin composition. This may result in a deterioration in the properties of the resulting insulating layer 230. In contrast, the use of a hydrogenated material can improve resistance to thermal degradation. This allows the properties of the insulating layer 230 to be maintained at a higher level.

[0072] Furthermore, the styrene-based elastomer may contain, for example, a styrene unit and at least one of a propylene unit and a butene unit. This allows the compatibility between the polypropylene as the base polymer (A) and the styrene-based elastomer to be stably improved. As a result, the polypropylene and the styrene-based elastomer can be uniformly mixed.

[0073] The content of styrene units in the styrene-based elastomer (content rate; hereinafter simply referred to as "styrene unit content") is not particularly limited, but the styrene unit content may be, for example, 5% by mass or more and 35% by mass or less. By setting the styrene unit content to 5% by mass or more and 35% by mass or less, it is possible to stably prevent the material from becoming excessively hard. This makes it possible to stably prevent separation and cracking between the polypropylene and the thermoplastic elastomer (C).

[0074] (olefin elastomer) The thermoplastic elastomer (C) may contain, for example, an olefin-based elastomer. This allows short-chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C). As a result, the compatibility between the base polymer (A) and the thermoplastic elastomer (C) can be improved.

[0075] The olefin elastomer as the thermoplastic elastomer (C) is, for example, a copolymer containing two olefin units, such as a copolymer containing an ethylene unit and an α-olefin unit having 3 or more carbon atoms, or a copolymer containing a propylene unit and an α-olefin unit having 4 or more carbon atoms.

[0076] Specifically, olefin elastomers include ethylene propylene rubber (EPR), very low density polyethylene (VLDPE), and propylene-1-butene copolymer (propylene-1-butene rubber (PBR)). Ethylene-1-butene copolymer (ethylene-1-butene rubber (EBR)) is a type of VLDPE.

[0077] The olefinic elastomer may contain, for example, at least one of a propylene unit and a butene unit. This allows the compatibility between the polypropylene as the base polymer (A) and the olefinic elastomer to be stably improved. As a result, the polypropylene and the olefinic elastomer can be uniformly mixed.

[0078] When the olefin elastomer contains ethylene units, the content of the ethylene units in the olefin elastomer is not particularly limited, but may be, for example, 5% by mass or more and 90% by mass or less, which allows the olefin elastomer to stably provide the softening effect and crystallization inhibition effect.

[0079] (Characteristics of thermoplastic elastomers) In this embodiment, the storage modulus of the thermoplastic elastomer (C) alone is, for example, 20 MPa or more and 500 MPa or less. The measurement method and conditions for the "storage modulus of the thermoplastic elastomer (C) alone" here are the same as those for the storage modulus of the insulating layer 230, which will be described later.

[0080] The MFR of the thermoplastic elastomer (C) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 5.0 g / 10 min or less, or 0.1 g / 10 min or more and 2.0 g / 10 min or less. The conditions for measuring the MFR of the thermoplastic elastomer (C) here are the same as those described for the MFR of the base polymer (A). When the MFR of the thermoplastic elastomer (C) is within the above range, the phase structure described below can be easily formed when the base polymer (A) and the thermoplastic elastomer (C) are mixed.

[0081] The thermoplastic elastomer (C) may, for example, have no melting point or may have a melting point lower than 165° C. This makes it possible to easily form a phase structure described below when the base polymer (A) and the thermoplastic elastomer (C) are mixed.

[0082] (Content of modified polymer (B) and thermoplastic elastomer (C)) The contents of the modified polymer (B) and thermoplastic elastomer (C) will be explained. Here, the total content of the resin component consisting of the base polymer (A), modified polymer (B), and thermoplastic elastomer (C) is taken as 100 parts by mass. The remainder of the resin component other than the modified polymer (B) and thermoplastic elastomer (C) is the base polymer (A).

[0083] In this embodiment, the content of the modified polymer (B) in the resin composition (i.e., the insulating layer 230) may be, for example, 1 part by mass or more and 10 parts by mass or less. By setting the content of the modified polymer (B) to 1 part by mass or more, it is possible to suppress a decrease in the insulating properties of the insulating layer 230. On the other hand, by setting the content of the modified polymer (B) to 10 parts by mass or less, it is possible to suppress a decrease in the formability of the insulating layer 230. This makes it possible to suppress a decrease in the insulating properties of the insulating layer 230 due to a decrease in formability.

[0084] The content of the thermoplastic elastomer (C) in the resin composition (i.e., the insulating layer 230) may be, for example, 10 parts by mass or more and 45 parts by mass or less. By setting the content of the thermoplastic elastomer (C) to 10 parts by mass or more, it is possible to prevent the elasticity of the insulating layer 230 from becoming excessively high, and to impart flexibility to the insulating layer 230. On the other hand, by setting the content of the thermoplastic elastomer (C) to 45 parts by mass or less, that is, by preventing excessive incorporation of the amorphous thermoplastic elastomer (C), it is possible to prevent a decrease in the insulating properties and mechanical properties that are originally required of polypropylene having a high melting point as the base polymer (A).

[0085] Furthermore, by setting the contents of the modified polymer (B) and the thermoplastic elastomer (C) within the above-mentioned ranges, a phase structure, which will be described later, can be easily formed.

[0086] In this way, by setting the content of each of the modified polymer (B) and the thermoplastic elastomer (C) within the above-mentioned ranges, it is possible to stably achieve both the desired distribution of elasticity and uniformity of insulating properties in the thickness direction of the insulating layer 230.

[0087] (inorganic filler) In this embodiment, the resin composition contains the modified polymer (B), and as described above, the space charge trapping effect of the modified polymer (B) can be uniformly obtained throughout the resin composition. This allows high insulating properties to be stably obtained without adding an inorganic filler. Therefore, in this embodiment, the resin composition does not need to contain an inorganic filler.

[0088] On the other hand, the resin composition may contain a trace amount of an inorganic filler.

[0089] Specifically, the resin composition contains an inorganic filler, and the content of the inorganic filler may be, for example, less than 1 part by mass when the total content of the resin components is 100 parts by mass. The lower limit of the content of the inorganic filler is not limited as long as the inorganic filler can be added.

[0090] Examples of inorganic fillers include magnesium oxide (MgO), silicon dioxide, zinc oxide, aluminum oxide, titanium oxide, zirconium oxide, carbon black, and mixtures of two or more of these.

[0091] The volume average particle diameter (MV) of the inorganic filler is not particularly limited, but may be, for example, 1 μm or less, or 700 nm or less, or 100 nm or less. The "volume average particle diameter (MV)" here refers to the particle diameter of the particles d i , the volume of the particle V i When this is the case, it can be calculated using the following formula: MV=Σ(V i d i ) / ΣV i The volume average particle size is measured using a dynamic light scattering particle size / particle size distribution measuring device.

[0092] The lower limit of the volume average particle size of the inorganic filler is not particularly limited, but from the viewpoint of stably forming the inorganic filler, the volume average particle size of the inorganic filler may be, for example, 1 nm or more, or 5 nm or more.

[0093] At least a portion of the inorganic filler may be surface-treated with a silane coupling agent, which can improve the adhesion at the interface between the inorganic filler and the base polymer (A), etc., and can improve the mechanical properties and insulating properties of the insulating layer 230.

[0094] (Crosslinking agent) In this embodiment, the resin component that constitutes the insulating layer 230 may be non-crosslinked from the viewpoint of recycling. In this case, the resin composition may not contain a crosslinking agent.

[0095] On the other hand, the resin composition may contain a trace amount of crosslinking agent to reduce the gel fraction (degree of crosslinking). Specifically, the resin composition may contain a crosslinking agent in such a content that the decomposition residue remaining in the insulating layer 230 due to the decomposition of the crosslinking agent in the insulating layer 230 is less than 300 ppm. When dicumyl peroxide is used as the crosslinking agent, the decomposition residue is, for example, cumyl alcohol, α-methylstyrene, or the like.

[0096] (Other additives) The resin composition may contain other additives as needed, such as antioxidants, lubricants, and colorants.

[0097] (3) Characteristics of the insulating layer In this embodiment, the insulating layer 230 formed from the insulating tape containing the resin composition described above does not have voids due to fusion bonding in the second heating step S244 described later. The insulating layer 230 of this embodiment has the following characteristics.

[0098] (3-1) Phase structure In this embodiment, the insulating layer 230 has a predetermined phase structure by mixing a base polymer (A), a modified polymer (B), and a thermoplastic elastomer (C).

[0099] Specifically, the inclusion of the modified polymer (B) in the insulating layer 230 forms a structure in which the base polymer (A) and the modified polymer (B) are compatible with each other, or a sea-island structure in which the modified polymer (B) is finely dispersed in the base polymer (A). The "compatible structure" here means that, for example, when the phase structure is observed with a transmission electron microscope, no phase separation can be confirmed and each component is uniformly dispersed.

[0100] The more finely the modified polymer (B) is dispersed in the insulating layer 230, the more the accumulation of space charge can be suppressed. From this viewpoint, a structure in which the resin components are compatible with each other may be formed in the insulating layer 230. Alternatively, when a sea-island structure is formed in the insulating layer 230, the diameter of the island phases formed from the modified polymer (B) may be less than 0.5 μm.

[0101] Furthermore, since the insulating layer 230 contains not only the base polymer (A) and the modified polymer (B) but also the thermoplastic elastomer (C), a sea-island structure in which the thermoplastic elastomer (C) is finely dispersed is formed in the above-mentioned phase structure of the two-component system in which the insulating layer 230 contains the base polymer (A) and the modified polymer (B).

[0102] By forming the above-described phase structure in the insulating layer 230, the polar groups in the modified polymer (B) can be uniformly dispersed in the insulating layer 230. This allows the space charge trapping effect to be obtained uniformly in the insulating layer 230.

[0103] Furthermore, by forming the above-described phase structure in the insulating layer 230, the thermoplastic elastomer (C) can be uniformly dispersed in the insulating layer 230. This makes it possible to obtain a stable distribution of elasticity in the insulating layer 230 according to the difference in cooling rate in the thickness direction of the insulating layer 230.

[0104] (Non-crosslinked or slightly crosslinked) In this embodiment, the insulating layer 230 is non-crosslinked or slightly crosslinked. Even if the insulating layer 230 is slightly crosslinked, the gel fraction (degree of crosslinking) is low. In this case, the insulating layer 230 is slightly crosslinked, for example, with less than 300 ppm of decomposition residue remaining in the insulating layer 230 due to the decomposed crosslinking agent. In this way, the insulating layer 230 is non-crosslinked or slightly crosslinked, which can improve recyclability.

[0105] (3-3) Characteristics In this embodiment, the insulating layer 230 has the following properties:

[0106] The term "outer sample" used below refers to a sheet taken from a position 0.3 mm from the outer peripheral surface of the insulating layer 230 toward the internal semiconductive layer 220 in the radial direction of the conductor connection portion 210. The term "inner sample" refers to a sheet taken from a position 0.3 mm from the inner peripheral surface of the insulating layer 230 toward the outer peripheral surface of the insulating layer 230 in the radial direction of the conductor connection portion 210. The "radial direction of the conductor connection portion 210" used here refers to the direction from the central axis of the conductor connection portion 210 toward the outer periphery.

[0107] (elasticity) In this embodiment, the elasticity of the insulating layer 230 varies in the thickness direction of the insulating layer 230 by performing a second heating step S244 which is an improved new manufacturing method described later.

[0108] Specifically, the ratio of the storage modulus of the inner sample of insulating layer 230 to the storage modulus of the outer sample of insulating layer 230 (hereinafter also referred to as "elastic modulus ratio") is, for example, 1.1 or more and 2.5 or less.

[0109] The "storage modulus" referred to here is measured by dynamic mechanical analysis (DMA) in accordance with JIS K7244-4:1999.

[0110] The dynamic viscoelasticity measurement is carried out under the following conditions. Measurement mode: Tensile mode Distortion: 0.08% Frequency: 10Hz Temperature range: 0°C to 200°C Heating rate: 10℃ / min

[0111] The "storage modulus of the outer sample" and the "storage modulus of the inner sample" in the definition of the elastic modulus ratio above are values ​​measured by the dynamic viscoelasticity measurement at 25°C. In the dynamic viscoelasticity measurement, the thickness of each sample is 0.5 mm.

[0112] In this embodiment, by setting the elastic modulus ratio to 1.1 or more, it is possible to make the outside of the insulating layer 230 relatively soft, while making the inside of the insulating layer 230 relatively hard. As a result, in this embodiment, it is possible to achieve both flexibility and strength of the insulating layer 230.

[0113] On the other hand, in this embodiment, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress excessive reduction in elasticity due to thermal degradation on the outside of the insulating layer 230. This makes it possible to suppress the occurrence of cracks in the insulating layer 230 due to impacts when the connecting power cable 10 is laid. Furthermore, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress the occurrence of voids due to stress differences within the insulating layer 230. This makes it possible to suppress a reduction in the dielectric breakdown strength (e.g., DC breakdown field strength) of the insulating layer 230.

[0114] For example, the elastic modulus of the insulating layer 230 may gradually decrease from the inner peripheral surface of the insulating layer 230 toward the outer peripheral surface of the insulating layer 230 in the radial direction of the conductor connection portion 210. By suppressing a sudden change in the elasticity of the insulating layer 230 in this way, it is possible to suppress the occurrence of cracks in the insulating layer 230 due to a difference in the elastic modulus.

[0115] The storage modulus of the inner sample of the insulating layer 230 is, for example, 650 MPa or more and 900 MPa or less. By setting the storage modulus of the inner sample to 650 MPa or more, it is possible to ensure the rigidity of the cable connection structure 20. On the other hand, by setting the storage modulus of the inner sample to 900 MPa or less, it is possible to prevent a decrease in the flexibility of the cable connection structure 20.

[0116] The storage modulus of the outer sample of the insulating layer 230 is, for example, 280 MPa or more and 670 MPa or less. By setting the storage modulus of the outer sample to 280 MPa or more, it is possible to prevent the outer side of the insulating layer 230 from becoming excessively soft due to thermal degradation or the like on the outer side of the insulating layer 230. This makes it possible to prevent the occurrence of cracks in the insulating layer 230 due to impacts when laying the connecting power cable 10 equipped with the cable connection structure 20. On the other hand, by setting the storage modulus of the outer sample to 670 MPa or less, it is possible to ensure the flexibility of the cable connection structure 20.

[0117] (insulating) In this embodiment, since the insulating layer 230 contains the modified polymer (B), the space charge trapping effect of the modified polymer (B) can be obtained uniformly throughout the insulating layer 230. As a result, the insulating properties of the insulating layer 230 are uniform in the thickness direction of the insulating layer 230.

[0118] Specifically, the ratio of the volume resistivity of the inner sample of insulating layer 230 to the volume resistivity of the outer sample of insulating layer 230 (hereinafter also referred to as "volume resistivity ratio") is, for example, 1.0 or more and 1.5 or less.

[0119] The "volume resistivity of the outer sample" and the "volume resistivity of the inner sample" are measured at a temperature of 90°C and in a DC electric field of 80 kV / mm.

[0120] In this embodiment, by setting the volume resistivity ratio to be 1.0 or more and 1.5 or less, the insulating layer 230 of the cable connection structure 20 as a whole can achieve the required sufficient insulating properties.

[0121] The volume resistivity of the outer sample of the insulating layer 230 and the volume resistivity of the inner sample of the insulating layer 230 measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm are, for example, 7.0×10 14 Ω·cm or more, or 3.6×10 15 It may be Ω·cm or more, or 5.0×10 15 It may be Ω·cm or more, or 7.0×10 15 It may be Ω·cm or more. In measuring the volume resistivity, the thickness of each sample shall be 0.2 mm.

[0122] The DC breakdown field strength of the outer sample of insulating layer 230 and the DC breakdown field strength of the inner sample of insulating layer 230 measured at a temperature of 90° C. may be, for example, 160 kV / mm or more, or 200 kV / mm or more. In measuring the DC breakdown field strength, the thickness of each sample is 0.2 mm.

[0123] (4) Method for manufacturing a cable connection structure, and method for manufacturing a connected power cable 2 and 3, a method for manufacturing the linked power cable 10 of this embodiment will be described. The method for manufacturing the linked power cable 10 includes a method for manufacturing the cable connection structure 20. Hereinafter, steps will be abbreviated as "S".

[0124] Below, in the manufacturing method of the connected power cable 10 of this embodiment, details of the steps not described in this disclosure can be carried out as a general manufacturing method for FJ, for example, as described in Patent Publication No. 2023-065809.

[0125] As shown in FIG. 2, the method for manufacturing the linking power cable 10 of this embodiment includes, for example, a preparation step S100 and a cable connection step S200.

[0126] (S100: Preparation process) First, a plurality of power cables 100 are prepared. Each power cable 100 is stripped stepwise from the tip of the conductor 110 in the opposite direction.

[0127] After the step stripping of each of the pair of power cables 100 is completed, the first power cable 100a is inserted, for example, into the semiconductive tube that constitutes the outer semiconductive layer 240, the metal tube 250, and the tube that constitutes the corrosion protection layer 260.

[0128] Furthermore, in this embodiment, the first power cable 100a is inserted in advance into the coil 540 used in the second heating step S244 described below.

[0129] (S200: Cable connection process) After the preparation step S100 is completed, the cable connection step S200 is performed. The cable connection step S200 of this embodiment includes, for example, a conductor connection step S210, an inner semiconductive layer formation step S220, a first heating step S224, an insulating layer formation step S230, an outer semiconductive layer formation step S240, a second heating step S244, and a post-process S250.

[0130] (S210: Conductor connection process) A conductor connection section 210 is formed by connecting the conductors 110 of the pair of power cables 100 together.

[0131] (S220: Internal semiconducting layer formation process) After the conductor connecting step S210, a semiconductive tape is wound around the outer periphery of the conductor connecting portion 210 so as to cover it, thereby forming an internal semiconductive layer 220 having semiconductivity.

[0132] (S224: 1st heating step) After the internal semiconductive layer forming step S220, the internal semiconductive layer 220 is heated. In the first heating step S224, the heating device 50 used in the second heating step S244 described later may be used. By performing the first heating step S224, the multiply wrapped semiconductive tapes in the internal semiconductive layer 220 are fused to each other.

[0133] (S230: Insulation layer formation process) After the first heating step S224, an insulating layer 230 having insulating properties is formed so as to cover the outer peripheries of the inner semiconductive layer 220, the cable inner semiconductive layer 120 and the cable insulating layer .

[0134] The insulating layer forming step S230 of this embodiment includes, for example, a tape preparing step S232 and a tape winding step S234.

[0135] (S232: Tape preparation process) First, an insulating tape containing the resin composition of this embodiment is prepared. The tape preparation step S232 may be performed in the preparation step S100.

[0136] In this embodiment, a resin component including a base polymer (A), a modified polymer (B), and a thermoplastic elastomer (C) is mixed (kneaded) with other additives (antioxidants, etc.) using a mixer to form a mixture. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-screw mixer, and a multi-screw mixer.

[0137] After the mixture is formed, the mixture is extruded into a tape shape using an extruder equipped with a T-die having a slit-shaped discharge port, thereby forming an insulating tape containing the resin composition that constitutes the insulating layer 230.

[0138] (S234: Tape winding process) After the tape preparation step S232 is completed, insulating tape is wrapped around the outer periphery of the internal semiconductive layer 220 and the outer periphery of the exposed portion of the cable insulating layer 130. This forms the insulating layer 230. The insulating layer 230 has an inner circumferential surface facing the internal semiconductive layer 220 and an outer circumferential surface opposite the inner circumferential surface.

[0139] (S240: Outer semiconducting layer formation process) After the insulating layer forming step S230, an outer semiconductive layer 240 having semiconductivity is formed so as to cover the outer periphery of the insulating layer 230.

[0140] Specifically, a semiconductive tube that has been passed through the first power cable 100a in advance is placed on the outer periphery of the cable insulating layer 130. After the semiconductive tube is placed, the semiconductive tube is thermally shrunk, thereby forming the outer semiconductive layer 240.

[0141] The outer semiconductive layer 240 may be formed by wrapping a semiconductive tape around the outer periphery of the insulating layer 230 .

[0142] As a result of the above, a cable core having the conductor connection portion 210, the inner semiconductive layer 220, the insulating layer 230 and the outer semiconductive layer 240 in the cable connection structure 20 is formed.

[0143] (S244: 2nd heating step) After the outer semiconductive layer forming step S240, the insulating layer 230 and the outer semiconductive layer 240 are heated and then cooled.

[0144] In this embodiment, the insulating layer 230 is heated and then cooled so that the ratio of the storage modulus of the inner sample of the insulating layer 230 to the storage modulus of the outer sample of the insulating layer 230 is 1.1 or more and 2.5 or less, and the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less.

[0145] Specifically, in the second heating step S244 of this embodiment, for example, a heating device 50 shown in FIG. 3 is used.

[0146] The heating device 50 includes, for example, a heating furnace (molding furnace) 510, a heater 520, a gas supply line 530, and a coil 540. The heating furnace 510 is configured as a cylindrical body having a hollow portion into which a cable core is inserted. The heater 520 is provided in the heating furnace 510 and configured to heat the cable core in the hollow portion of the heating furnace 510. The gas supply line 530 is provided in the hollow portion of the heating furnace 510 along the axial direction of the heating furnace 510. The gas supply line 530 is configured to seal a gas such as nitrogen gas or air in the hollow portion of the heating furnace 510 and to be able to pressurize the hollow portion of the heating furnace 510. The first power cable 100a is inserted into the coil 540 in advance, and the coil 540 is moved to the vicinity of the conductor connection portion 210 in the second heating step S244. The coil 540 is spirally wound around the outer periphery near the conductor connection portion 210. Coil 540 is configured to allow an alternating current to flow therethrough.

[0147] In the second heating step S244, the outer periphery of the cable core is first covered with a group of presser tubes. The cable core in this state is set in the heating device 50.

[0148] After the cable core is set in the heating device 50, a gas such as nitrogen gas or air is supplied from a gas supply line 530 to the cable core in the hollow portion of the heating furnace 510 to pressurize it, while the cable core is heated by the heater 520. The heater 520 heats the insulating layer 230 from a region close to the outer peripheral surface of the insulating layer 230.

[0149] Furthermore, in this embodiment, the conductor connection portion 210 is heated by electromagnetic induction by passing an alternating current through the coil 540 while the insulating layer 230 is heated from a region close to the outer circumferential surface of the insulating layer 230 by the heater 520 described above.

[0150] Here, "electromagnetic induction heating" refers to heating of the conductor connection part 210 by heat generated by eddy current loss in the conductor connection part 210 due to electromagnetic induction and heat generated by hysteresis loss in the conductor connection part 210. Electromagnetic induction heating can heat the conductor connection part 210 of the cable core without contact. Electromagnetic induction heating heats not only the conductor connection part 210 but also the conductor 110 around the conductor connection part 210.

[0151] The above-described electromagnetic induction heating of the conductor connection portion 210 allows the insulating layer 230 to be heated not only from a region close to the outer peripheral surface of the insulating layer 230, but also from a region close to the inner peripheral surface of the insulating layer 230. This allows the inside of the insulating layer 230 to be stably heated without the need to excessively raise the temperature at which the heater 520 heats the region close to the outer peripheral surface of the insulating layer 230. By not raising the heating temperature by the heater 520 excessively, excessive heating of the outside of the insulating layer 230 can be prevented, and thermal deterioration of the outside of the insulating layer 230 can be suppressed. Furthermore, stably heating the inside of the insulating layer 230 by electromagnetic induction heating of the conductor connection portion 210 allows the insulating tape on the inside of the insulating layer 230 to be stably fused.

[0152] As described above, by performing electromagnetic induction heating of the conductor connection portion 210, in principle, it is possible to reduce the temperature difference between the outside and inside of the insulating layer 230.

[0153] However, during heating in the second heating step S244 of this embodiment, a temperature difference is intentionally created between the outside and inside of the insulating layer 230 within a temperature range that suppresses thermal degradation of the outside of the insulating layer 230.

[0154] Specifically, during heating in the second heating step S244 of this embodiment, the temperature at a position 0.3 mm from the outer peripheral surface of the insulating layer 230 toward the internal semiconducting layer 220, i.e., the position where the outer sample of the insulating layer 230 is taken, is set to, for example, 220°C or higher and 285°C or lower.

[0155] By setting the temperature at the collection position of the outer sample of the insulating layer 230 to 220°C or higher, the cooling rate at the outer side of the insulating layer 230 can be increased during cooling, which will be described later. That is, the outer side of the insulating layer 230 can be rapidly cooled. This makes it possible to suppress excessive crystallization at the outer side of the insulating layer 230. As a result, the elasticity of the outer side of the insulating layer 230 can be reduced.

[0156] On the other hand, by setting the temperature at the location where the outer sample of the insulating layer 230 is taken to 285°C or less, it is possible to suppress thermal degradation of the outer side of the insulating layer 230. This makes it possible to suppress excessive loss of elasticity and excessive loss of insulating properties on the outer side of the insulating layer 230. As a result, it is possible to obtain the insulating properties and mechanical characteristics required for the cable connection structure 20.

[0157] During heating in the second heating step S244 of this embodiment, the temperature at a position 0.3 mm from the inner surface of the insulating layer 230 toward the outer surface, i.e., the position where the inner sample of the insulating layer 230 is taken, is set to, for example, greater than 170°C and less than 190°C.

[0158] By setting the temperature at the sampling position of the inner sample of the insulating layer 230 to 170°C or higher, the temperature inside the insulating layer 230 can be set to the melting point of the base polymer (A) or higher. This allows the insulating tape inside the insulating layer 230 to be stably fused.

[0159] On the other hand, by setting the temperature at the sampling position of the inner sample of the insulating layer 230 to 190°C or less, a temperature difference can be generated between the outside and inside of the insulating layer 230. As a result, during cooling, which will be described later, the outside of the insulating layer 230 can be rapidly cooled, while the inside of the insulating layer 230 can be slowly cooled. By slowly cooling the inside of the insulating layer 230, the base polymer (A) inside the insulating layer 230 can be crystallized. As a result, the elasticity of the inside of the insulating layer 230 can be made higher than the elasticity of the outside of the insulating layer 230.

[0160] Furthermore, during heating in the second heating step S244 of this embodiment, the temperature difference obtained by subtracting the temperature at the collection position of the outer sample of the insulating layer 230 from the temperature at the collection position of the outer sample of the insulating layer 230 may be set to, for example, 40°C or more and 105°C or less. This allows the outer side of the insulating layer 230 to be rapidly cooled while the inner side of the insulating layer 230 is slowly cooled during cooling, which will be described later. As a result, the elastic modulus ratio of the insulating layer 230 can be set to 1.1 or more and 2.5 or less, and the volume resistivity ratio of the insulating layer 230 can be set to 1.0 or more and 1.5 or less.

[0161] In this embodiment, the heating time in the second heating step S244 is not particularly limited, but is set so as to fuse the multiple wrapped insulating tapes together in the insulating layer 230. Specifically, the heating time in the second heating step S244 may be, for example, from 1 hour to 10 hours, or from 2 hours to 5 hours. By setting the heating time to 1 hour or more, or 2 hours or more, the insulating tapes can be stably fused. On the other hand, by setting the heating time to 10 hours or less, or 5 hours or less, thermal degradation of the insulating layer 230 can be suppressed.

[0162] By the heating in the second heating step S244, the inner semiconductive layer 220, the insulating layer 230, and the outer semiconductive layer 240 are fused together and integrated.

[0163] After the above-described heating, the coil 540 is cut and removed, and the cable core is taken out of the heating device 50. Next, the presser tubes covering the cable core are removed. This allows the cable core to cool naturally, for example, in the atmosphere. Note that the cable core may be cooled using a predetermined cooling means so as to obtain the cooling rate described below.

[0164] At this time, as described above, during heating in the second heating step S244, a temperature difference is intentionally created between the outside and inside of the insulating layer 230 within a temperature range that suppresses thermal deterioration of the outside of the insulating layer 230, so that during cooling, the outside of the insulating layer 230 is cooled rapidly while the inside of the insulating layer 230 is cooled slowly.

[0165] Specifically, at the location where the outer sample of the insulating layer 230 is taken, the cooling rate (temperature drop rate) at a temperature of 110°C may be, for example, 30°C / min or more, or 75°C / min or more, or 100°C / min or more. This makes it possible to suppress excessive crystallization on the outer side of the insulating layer 230. As a result, it is possible to reduce the elasticity of the outer side of the insulating layer 230. The "cooling rate at a temperature of 110°C" here is calculated as the absolute value of the gradient of temperature with respect to time at a temperature of 110°C.

[0166] At this time, the cooling rate at a temperature of 110°C at the position where the outer sample of the insulating layer 230 is taken may be, for example, 310°C / min or less. This makes it possible to suppress excessive variations in the crystallinity in the thickness direction of the insulating layer 230. As a result, it is possible to suppress the occurrence of excessive differences in elasticity in the thickness direction of the insulating layer 230.

[0167] On the other hand, the cooling rate (temperature drop rate) at the collection position of the inner sample of the insulating layer 230 is not limited as long as it is slower than the cooling rate at the collection position of the outer sample of the insulating layer 230. However, the cooling rate at the temperature of 110°C at the collection position of the inner sample of the insulating layer 230 may be, for example, 1°C / min or more and 10°C / min or less, or 2°C / min or more and 8°C / min or less.

[0168] By cooling after heating in the second heating step S244, the elastic modulus ratio of the insulating layer 230 can be set to 1.1 or more and 2.5 or less, and the volume resistivity ratio of the insulating layer 230 can be set to 1.0 or more and 1.5 or less.

[0169] (S250: Post-process) After the second heating step S244 is completed, the water-absorbing tape layer 242, the metal pipe 250, and the anticorrosion layer 260 are formed in this order to cover the outer periphery of the outer semiconductive layer 240. Then, the cover portion 270 is formed on the axial end of the anticorrosion layer 260.

[0170] In this manner, the linked power cable 10 of this embodiment is manufactured.

[0171] (5) Summary of this embodiment According to this embodiment, one or more of the following effects are achieved.

[0172] (a) In this embodiment, during heating in the second heating step S244, a temperature difference is generated between the outside and inside of the insulating layer 230 within a temperature range that suppresses thermal degradation of the outside of the insulating layer 230. As a result, during subsequent cooling, the outside of the insulating layer 230 can be rapidly cooled while the inside of the insulating layer 230 is gradually cooled.

[0173] By such slow cooling inside the insulating layer 230 and rapid cooling outside the insulating layer 230, a predetermined amount of the base polymer (A) is crystallized inside the insulating layer 230, whereas the resin component is solidified in a nearly amorphous state outside the insulating layer 230. This allows the elasticity of the insulating layer 230 to vary in the thickness direction of the insulating layer 230.

[0174] On the other hand, since the insulating layer 230 contains a predetermined amount of modified polymer (B), the polar groups in the modified polymer (B) can be uniformly dispersed in the insulating layer 230. This allows the space charge trapping effect of the modified polymer (B) to be uniformly obtained in the insulating layer 230. That is, even if the crystallinity of the insulating layer 230 is distributed in the thickness direction of the insulating layer 230 as described above, variations in the insulating properties due to the distribution of the crystallinity can be suppressed. As a result, the insulating properties of the insulating layer 230 can be made uniform in the thickness direction of the insulating layer 230.

[0175] As described above, according to this embodiment, it is possible to obtain a desired distribution of elasticity in the thickness direction of the insulating layer 230 while making the insulating properties of the insulating layer 230 uniform in the thickness direction of the insulating layer 230. As a result, it is possible to obtain a connecting power cable 10 equipped with a cable connection structure 20 in which the flexibility, strength, and insulating properties of the insulating layer 230 are improved.

[0176] (b) In this embodiment, the ratio of the storage modulus of the inner sample of the insulating layer 230 to the storage modulus of the outer sample of the insulating layer 230 can be set to 1.1 or more and 2.5 or less.

[0177] By setting the elastic modulus ratio to 1.1 or more, the outside of the insulating layer 230 can be made relatively soft, while the inside of the insulating layer 230 can be made relatively hard. By making the outside of the insulating layer 230 relatively soft, the flexibility of the cable connection structure 20 and the connecting power cable 10 can be improved. For example, excessive restrictions on the reel diameter when winding the connecting power cable 10 around a reel can be avoided. Furthermore, by making the inside of the insulating layer 230 relatively hard, the rigidity of the cable connection structure 20 and the connecting power cable 10 can be ensured. In this way, it is possible to achieve both flexibility and strength of the insulating layer 230.

[0178] On the other hand, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress excessive reduction in elasticity due to thermal degradation on the outside of the insulating layer 230. This makes it possible to suppress the occurrence of cracks in the insulating layer 230 due to impacts when the connecting power cable 10 is laid. Furthermore, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress the occurrence of voids due to stress differences within the insulating layer 230. This makes it possible to suppress a reduction in the dielectric breakdown strength (e.g., DC breakdown field strength) of the insulating layer 230.

[0179] (c) In this embodiment, by uniformly dispersing a predetermined amount of polar groups in the modified polymer (B) that trap space charges throughout the insulating layer 230, the ratio of the volume resistivity of an inner sample of the insulating layer 230 to the volume resistivity of an outer sample of the insulating layer 230 can be set to 1.0 or more and 1.5 or less. For example, even if the crystallinity of the outer side of the insulating layer 230 becomes relatively low due to rapid cooling of the outer side of the insulating layer 230 during cooling after the temperature difference in the second heating step S244 is generated, it is possible to suppress a decrease in the insulating properties of the outer side of the insulating layer 230. As a result, the insulating layer 230 of the cable connection structure 20 as a whole can achieve the required sufficient insulating properties.

[0180] (d) In this embodiment, even when the thickness of the insulating layer 230 is set to 3 mm or more, it is possible to obtain a desired distribution of elasticity in the thickness direction of the insulating layer 230 while making the insulating properties of the insulating layer 230 uniform in the thickness direction of the insulating layer 230. Therefore, even when a connecting power cable 10 including the cable connection structure 20 of this embodiment is used in high-voltage applications, it is possible to stably achieve both the flexibility of the insulating layer 230 and the insulating properties of the insulating layer 230.

[0181] <Other Embodiments of the Present Disclosure> Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present disclosure.

[0182] In the above embodiment, the connecting power cable 10 is described as being configured to be laid on the bottom of the water, but the connecting power cable 10 may also be configured to be laid on land, etc. [Example]

[0183] Next, examples according to the present disclosure will be described. These examples are examples of the present disclosure, and the present disclosure is not limited to these examples.

[0184] (1) Experiment 1 (1-1) Manufacturing of cable connection structures The cable connection structures of samples B1, A2 to A5, B6 and B7 were manufactured as follows.

[0185] <Sample A2 to A5> A pair of power cables was prepared, each having a conductor, a cable inner semiconductive layer, a cable insulating layer, and a cable outer semiconductive layer. 2The base polymer of the cable insulation layer was random PP. The thicknesses of the inner cable semiconductive layer, the cable insulation layer, and the outer cable semiconductive layer were 0.5 mm, 9 mm, and 0.5 mm, respectively. Each power cable was peeled in stages, starting from the tip of the conductor and working in the opposite direction.

[0186] After the preparation process, a conductor connection was formed by connecting the conductors of a pair of power cables. After the conductor connection process, a semiconductive tape containing random PP was wound around the conductor connection to form an internal semiconductive layer. The thickness of the internal semiconductive layer was set to 0.5 mm.

[0187] After the internal semiconductive layer forming step, the internal semiconductive layer was heated to fuse the multiply wound semiconductive tapes together in the internal semiconductive layer.

[0188] Next, an insulating layer forming step was carried out. An insulating tape containing a resin composition containing the following materials was prepared.

[0189] (Base polymer (A)) Random Polypropylene (r-PP): Stereoregularity: isotactic, Density: 0.9g / ml, Melting point: 150℃, Heat of fusion: 60J / g, Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 1150 MPa Content in resin component: 70 parts by mass

[0190] (Modified polymer (B)) Maleic anhydride modified polypropylene (MAH-PP): Maleic anhydride modification amount: 5% by mass, Melting point: 160℃, Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 1300 MPa Content in resin component: 5 parts by mass

[0191] (Thermoplastic elastomer (C)) Styrene-ethylene-butylene-styrene block copolymer (SEBS): Styrene unit content: 25% by mass, Melting point: None, Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 120 MPa Content in resin component: 25 parts by mass

[0192] After the tape preparation step, insulating tape was wrapped around the outer periphery of the internal semiconducting layer and the outer periphery of the exposed portion of the cable insulating layer to form an insulating layer with a thickness of 9 mm.

[0193] After the insulating layer formation step, the outer periphery of the insulating layer was covered with a semiconductive tube containing random PP to form an outer semiconductive layer with a thickness of 0.5 mm.

[0194] After the outer semiconductive layer forming step, a second heating step was carried out as follows.

[0195] In the second heating step, thermocouples were placed (pierced) at a position 0.3 mm from the outer surface of the insulating layer toward the internal semiconductive layer (i.e., the position from which the outer sample was taken) and at a position 0.3 mm from the outer surface of the insulating layer toward the internal semiconductive layer (i.e., the position from which the inner sample was taken).

[0196] Next, with the outer periphery of the cable core covered with the presser tube group, the insulating layer and the outer semiconductive layer were heated using the above-mentioned heating device under the following conditions.

[0197] Electromagnetic induction heating of conductor joints: Implementation Temperature at a position 0.3 mm from the outer surface of the insulating layer toward the inner semiconducting layer (hereinafter referred to as "outer temperature"): 220°C or higher and 285°C or lower Temperature at a position 0.3 mm from the inner surface of the insulating layer toward the outer surface (hereinafter referred to as "inner temperature"): 180°C Cooking time: 4 hours

[0198] The outer and inner temperatures of each sample during heating in the second heating step are shown in Table 1. Heating by the heater of the heating device and electromagnetic induction heating of the conductor connection part by passing an alternating current through the coil were adjusted so that the outer and inner temperatures of each sample shown in Table 1 were obtained.

[0199] After the heating, the coil was cut and removed, and the cable core was taken out of the heating device. Next, the presser tubes covering the cable core were removed. This allowed the cable core to cool naturally in the air.

[0200] In this manner, cable connection structures of samples A2 to A5 were manufactured.

[0201] (Sample B1) The cable connection structure of Sample B1 was manufactured in the same manner as Sample A3, except that the outer temperature during heating in the second heating step was set to 180°C.

[0202] (Sample B6) The cable connection structure of Sample B6 was manufactured in the same manner as Sample A3, except that the outer temperature during heating in the second heating step was set to 290°C.

[0203] (Sample B7) The cable connection structure of Sample B7 was manufactured in the same manner as Sample A3, except that induction heating was not performed during the second heating step and the outer temperature was set to 300°C.

[0204] (1-2) Evaluation The cable connection structures of samples B1, A2 to A5, B6 and B7 were evaluated as follows.

[0205] (Temperature transition) The temperature transition during the second heating step was measured on the outside and inside of the insulating layer of each sample using the above-mentioned thermocouples.

[0206] (Sample collection after the second heating step) The insulation layer of each sample cable connection structure was thinly sliced ​​in the circumferential direction. Here, "circumferential direction" refers to the direction along the outer periphery of the insulation layer. Using the above-described slicing method, outer samples of the insulation layer were taken from a position 0.3 mm from the outer periphery of the insulation layer toward the conductor. Inner samples of the insulation layer were taken from a position 0.3 mm from the inner periphery toward the outer periphery of the insulation layer. The size of each sample for dynamic viscoelasticity measurements was 5 mm long, 42 mm wide, and 0.5 mm thick. The size of each sample for volume resistivity and DC breakdown field strength measurements was 50 mm long, 50 mm wide, and 0.2 mm thick.

[0207] (storage modulus) The storage modulus of the insulating layer in each sample was measured by dynamic viscoelasticity measurement (DMA) in accordance with JIS K7244-4:1999 under the following conditions. Measuring device: DVA-200 manufactured by IT Measurement and Control Co., Ltd. Measurement mode: Tensile mode Distortion: 0.08% Frequency: 10Hz Temperature range: 0°C to 200°C Heating rate: 10℃ / min

[0208] At this time, the storage modulus of the outer sample and the elastic modulus of the inner sample were measured at 25°C by the above-mentioned DMA.

[0209] (volume resistivity) The volume resistivity of the insulating layer in each sample was measured as follows. First, flat electrodes with a diameter of 25 mm were placed on the first surface of the sheet serving as the outer or inner sample and on the second surface opposite the first surface. After the electrodes were placed, the sheet was immersed in silicone oil at a temperature of 90°C. In this state, a DC electric field of 80 kV / mm was applied to the sheet. This allowed the volume resistivity to be measured.

[0210] (DC breakdown field strength) The DC breakdown field strength of the insulating layer of each sample was measured as follows. Specifically, as in the measurement of volume resistivity, flat electrodes with a diameter of 25 mm were placed on the first surface of the sheet serving as the outer or inner sample and on the second surface opposite the first surface. After the electrodes were placed, the sheet was immersed in silicone oil at a temperature of 90°C. In this state, the applied voltage was increased at a rate of 4 kV / min. The DC breakdown field strength of the sheet was then measured when the sheet reached dielectric breakdown. For both the outer and inner samples, a DC breakdown field strength of 160 kV / mm or greater was evaluated as A (good). On the other hand, a DC breakdown field strength of less than 160 kV / mm for at least either the outer or inner sample was evaluated as B (poor).

[0211] (1-3) Results The results of the evaluation of each sample will be explained with reference to Figures 4 and 5 and Table 1 below.

[0212] [Table 1]

[0213] <Comparison of temperature changes> The temperature transitions of Sample B1 and Sample A3 are compared with each other with reference to Table 1, Figures 4 and 5. In Figures 4 and 5, the start of cooling is set to "0 s (0 seconds)."

[0214] (Sample B1) As shown in Table 1 and Figure 5, during the second heating step for Sample B1, both the outer and inner temperatures of the insulating layer were maintained at 180°C by adjusting the heating by the heater of the heating device and the electromagnetic induction heating of the conductor connection portion. Therefore, during cooling after heating in the second heating step for Sample B1, both the outer and inner temperatures of the insulating layer decreased gradually. Thus, for Sample B1, the cooling rate of the base polymer on the outer side of the insulating layer was close to the cooling rate of the base polymer on the inner side of the insulating layer. Specifically, the cooling rate at a temperature of 110°C at the sample collection position on the outer side of the insulating layer was approximately 8°C / min, and the cooling rate at a temperature of 110°C at the sample collection position on the inner side of the insulating layer was approximately 4°C / min.

[0215] (Sample A3) In contrast, as shown in Table 1 and Figure 4, during heating in the second heating step for sample A3, the heating by the heater of the heating device and the electromagnetic induction heating of the conductor connection portion were adjusted to set the outside temperature of the insulating layer to 250°C and the inside temperature of the insulating layer to 180°C, resulting in a temperature difference of 70°C between the outside and inside of the insulating layer.

[0216] During cooling after heating in the second heating step for sample A3, the temperature inside the insulating layer decreased gradually, while the temperature outside the insulating layer decreased rapidly. As a result, the base polymer on the outside of the insulating layer cooled faster than the base polymer on the inside of the insulating layer. Specifically, the cooling rate at the temperature of 110°C at the sample collection position inside the insulating layer was approximately 4°C / min, while the cooling rate at the temperature of 110°C at the sample collection position outside the insulating layer was approximately 31°C / min.

[0217] <Comparison of each characteristic> (Sample B1) When Sample B1 was heated in the second heating step, induction heating was performed as described above, but both the outer and inner temperatures of the insulating layer were 180° C. Therefore, when Sample B1 was cooled after heating in the second heating step, both the outer and inner sides of the insulating layer were gradually cooled.

[0218] Therefore, in sample B1, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was close to 1. However, in sample B1, the ratio of the storage modulus of the inner sample to the storage modulus of the outer sample was also close to 1.

[0219] In sample B1, the degree of crystallinity of the insulating layer was high and uniform in the thickness direction due to the slow cooling of both the outer and inner sides of the insulating layer, which is thought to be why the elasticity of the insulating layer in sample B1 was high and uniform in the thickness direction.

[0220] (Samples B6 and B7) During heating in the second heating step for samples B6 and B7, the temperature inside the insulating layer was 180°C, but the temperature outside the insulating layer was higher than 285°C.

[0221] Therefore, for samples B6 and B7, the ratio of the storage modulus of the inner sample to that of the outer sample was greater than 2.5. For samples B6 and B7, the ratio of the volume resistivity of the inner sample to that of the outer sample was greater than 1.5. Furthermore, for samples B6 and B7, the DC breakdown field strength was less than 160 kV / mm.

[0222] In samples B6 and B7, the temperature outside the insulating layer was too high, causing thermal degradation of the outside of the insulating layer, which is thought to have resulted in excessive reductions in elasticity and insulating properties on the outside of the insulating layer.

[0223] (Samples A2 to A5) In contrast, in samples A2 to A5, the outer temperature of the insulating layer was set to 220° C. or higher and 285° C. or lower, and the inner temperature of the insulating layer was set to 180° C. As a result, when samples A2 to A5 were cooled after heating in the second heating step, the inner side of the insulating layer was gradually cooled and the outer side of the insulating layer was rapidly cooled.

[0224] As a result, for samples A2 to A5, the ratio of the storage modulus of the inner sample to the storage modulus of the outer sample was 1.1 or more and 2.5 or less. For samples A2 to A5, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was 1.0 or more and 1.5 or less. For samples A2 to A5, the DC breakdown field strength was 160 kV / mm or more.

[0225] From the results of samples A2 to A5 above, it was confirmed that it is possible to obtain a cable connection structure in which the desired distribution of elasticity in the thickness direction of the insulating layer is achieved while the insulating properties of the insulating layer are made uniform in the thickness direction of the insulating layer.

[0226] (2) Experiment 2 (2-1) Manufacturing of cable connection structures The following cable connection structures of Samples A6 to A10 were manufactured. During the second heating step of Samples A6 to A10, the inside and outside temperatures of the insulating layer were the same as those of Sample A3.

[0227] (Sample A6) The cable connection structure of sample A6 was manufactured in the same manner as sample A3, except that the contents of r-PP, MAH-PP, and SEBS in the resin components of the insulating layer were 70 parts by mass, 1 part by mass, and 29 parts by mass, respectively.

[0228] (Sample A7) The cable connection structure of sample A7 was manufactured in the same manner as sample A3, except that the contents of r-PP, MAH-PP, and SEBS in the resin components of the insulating layer were 70 parts by mass, 10 parts by mass, and 20 parts by mass, respectively.

[0229] (Sample A8) The cable connection structure of sample A8 was manufactured in the same manner as sample A3, except that the r-PP content, MAH-PP content, and SEBS content in the resin component of the insulating layer were 85 parts by mass, 5 parts by mass, and 10 parts by mass, respectively.

[0230] (Sample A9) The cable connection structure of sample A9 was manufactured in the same manner as sample A3, except that the contents of r-PP, MAH-PP, and SEBS in the resin components were 55 parts by mass, 5 parts by mass, and 40 parts by mass, respectively.

[0231] (Sample A10) The cable connection structure of Sample A10 was manufactured in the same manner as Sample A3, except that the insulating layer contained the following olefin-based elastomer instead of SEBS as the thermoplastic elastomer (C).

[0232] Ethylene Propylene Rubber (EPR): Ethylene unit content: 25% by mass, Melting point: None, Heat of fusion: None Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 80 MPa Content in resin component: 25 parts by mass

[0233] (2-2) Results The insulating layers in the cable connection structures of samples A6 to A10 satisfied the following characteristics.

[0234] Ratio of storage modulus of inner sample to storage modulus of outer sample: 1.1 to 2.5 Storage modulus of outer sample: 280 MPa or more and 670 MPa or less Storage modulus of inner sample: 650 MPa or more and 900 MPa or less Ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample: 1.0 to 1.5 Volume resistivity of outer and inner samples: 7.0 x 10 14 Ω cm or more DC breakdown field strength of outer and inner specimens: 160 kV / mm or more

[0235] From the results of samples A6 to A10 above, it was confirmed that even if the composition of the insulating layer is different from that of sample A3, by slowly cooling the inside of the insulating layer while rapidly cooling the outside of the insulating layer, it is possible to obtain a cable connection structure in which the desired distribution of elasticity in the thickness direction of the insulating layer is achieved while the insulating properties of the insulating layer are uniform in the thickness direction of the insulating layer.

[0236] <Additional Notes> The following appendix describes aspects of the present disclosure. The aspects referenced by the numbers in brackets [ ] to which the appendix follows correspond to the aspects described in <Embodiments of the present disclosure>.

[0237]

[10] The styrene elastomer contains a styrene unit and at least one of a propylene unit and a butene unit. The cable connection structure according to [3] above.

[0238]

[11] The olefin-based elastomer contains at least one of a propylene unit and a butene unit. The cable connection structure according to [4] above.

[0239]

[12] The volume resistivity of the outer sample and the volume resistivity of the inner sample were each 7.0×10 14 Ω·cm or more, Here, the volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90°C and a DC electric field of 80 kV / mm. A cable connection structure according to any one of [1] to [6],

[10] and

[11] above. [Explanation of symbols]

[0240] 10 Connecting power cable 20 Cable connection structure 50 Heating device 100 Power Cable 100a First power cable 100b Second power cable 110 Conductor 120 Cable inner semiconductive layer 130 Cable insulation layer 140 Cable outer semiconductive layer 150 Cable Metal Tube 160 Cable sheath 210 Conductor connection 220 Internal semiconductive layer 230 Insulating layer 240 outer semiconductive layer 242 Water-absorbing tape layer 250 metal tube 260 Anti-corrosion layer 270 Cover 510 Heating Furnace 520 Heater 530 Gas Supply Line 540 coil

Claims

1. a conductor connection portion connecting the conductors of the pair of power cables; an inner semiconductive layer that is provided so as to cover an outer periphery of the conductor connection portion and has semiconductivity; an insulating layer provided so as to cover an outer periphery of the internal semiconductive layer, having insulating properties, and having an inner circumferential surface facing the internal semiconductive layer and an outer circumferential surface opposite to the inner circumferential surface; an outer semiconductive layer that is provided so as to cover the outer periphery of the insulating layer and has semiconductivity; Equipped with The insulating layer is a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, a ratio of the storage modulus of an inner sample of the insulating layer to the storage modulus of an outer sample of the insulating layer is 1.1 or more and 2.5 or less; a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the inner semiconducting layer; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. Cable connection structure.

2. When the total content of the base polymer, the modified polymer, and the thermoplastic elastomer in the insulating layer is 100 parts by mass, the content of the modified polymer in the insulating layer is 1 part by mass or more and 10 parts by mass or less; The content of the thermoplastic elastomer in the insulating layer is 10 parts by mass or more and 45 parts by mass or less. The cable connection structure according to claim 1 .

3. The thermoplastic elastomer includes a styrene-based elastomer. The cable connection structure according to claim 1 or 2.

4. The thermoplastic elastomer includes an olefin-based elastomer. The cable connection structure according to claim 1 or 2.

5. the storage modulus of the inner sample of the insulating layer is 650 MPa or more and 900 MPa or less; The storage modulus of the outer sample of the insulating layer is 280 MPa or more and 670 MPa or less. The cable connection structure according to claim 1 or 2.

6. The thickness of the insulating layer is 3 mm or more. The cable connection structure according to claim 1 or 2.

7. The cable connection structure according to claim 1 or 2 is provided. Interlocking power cable.

8. forming a conductor connection portion by connecting the conductors of the pair of power cables; forming an inner semiconductive layer having semiconductivity so as to cover an outer periphery of the conductor connection portion; forming an insulating layer having insulating properties so as to cover an outer periphery of the internal semiconducting layer; forming an outer semiconductive layer having semiconductivity so as to cover an outer periphery of the insulating layer; heating the insulating layer and the outer semiconducting layer and then cooling; Equipped with The step of forming the insulating layer includes: preparing an insulating tape containing a resin composition; a step of winding the insulating tape around an outer periphery of the internal semiconductive layer to form an inner periphery surface of the insulating layer facing the internal semiconductive layer and an outer periphery surface opposite to the inner periphery surface; and In the step of preparing the insulating tape, The resin composition includes: a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; preparing an insulating tape comprising: The step of heating and then cooling the insulating layer and the outer semiconducting layer comprises: the insulating layer is heated and then cooled so that a ratio of the storage elastic modulus of an inner sample of the insulating layer to that of an outer sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to that of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the inner semiconducting layer; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. A method for manufacturing a cable connection structure.

9. The step of heating and then cooling the insulating layer and the outer semiconducting layer comprises: The insulating layer is heated from a region close to the outer circumferential surface of the insulating layer, and the conductor connection portion is heated by electromagnetic induction heating, thereby heating the insulating layer also from a region close to the inner circumferential surface of the insulating layer. A method for manufacturing the cable connection structure according to claim 8.

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